This invention relates to an improved catalyst for the conversion of hydrocarbons, and more specifically for the catalytic reforming of gasoline-range hydrocarbons.
The subject of the present invention is a novel dual-function catalytic composite, characterized by a combination of three or more metals in specified concentrations on the finished catalyst, and its use in hydrocarbon conversion. Catalysts having both a hydrogenation-dehydrogenation function and a cracking function are used widely in many applications, particularly in the petroleum and petrochemical industry, to accelerate a wide spectrum of hydrocarbon-conversion reactions. The cracking function generally relates to an acid-action material of the porous, adsorptive, refractory-oxide type which is typically utilized as the support or carrier for a heavy-metal component, such as the Group VIII(IUPAC 8-10) metals, which primarily contribute the hydrogenation-dehydrogenation function. Other metals in combined or elemental form can influence one or both of the cracking and hydrogenation-dehydrogenation functions.
In another aspect, the present invention comprehends improved processes that emanate from the use of the novel catalyst. These dual-function catalysts are used to accelerate a wide variety of hydrocarbon-conversion reactions such as dehydrogenation, hydrogenation, hydrocracking, hydrogenolysis, isomerization, desulfurization, cyclization, alkylation, polymerization, cracking, and hydroisomerization. In a specific aspect, an improved reforming process utilizes the subject catalyst to increase selectivity to gasoline and aromatics products.
Catalytic reforming involves a number of competing processes or reaction sequences. These include dehydrogenation of cyclohexanes to aromatics, dehydroisomerization of alkylcyclopentanes to aromatics, dehydrocyclization of an acyclic hydrocarbon to aromatics, hydrocracking of paraffins to light products boiling outside the gasoline range, dealkylation of alkylbenzenes and isomerization of paraffins. Some of the reactions occurring during reforming, such as hydrocracking which produces light paraffin gases, have a deleterious effect on the yield of products boiling in the gasoline range. Process improvements in catalytic reforming thus are targeted toward enhancing those reactions effecting a higher yield of the gasoline fraction at a given octane number.
It is of critical importance that a dual-function catalyst exhibit the capability both to initially perform its specified functions efficiently and to perform them satisfactorily for prolonged periods of time. The parameters used in the art to measure how well a particular catalyst performs its intended functions in a particular hydrocarbon reaction environment are activity, selectivity and stability. In a reforming environment, these parameters are defined as follows:
1) Activity is a measure of the ability of the catalyst to convert hydrocarbon reactants to products at a designated severity level, with severity level representing a combination of reaction conditions: temperature, pressure, contact time, and hydrogen partial pressure. Activity typically is designated as the octane number of the pentanes and heavier (xe2x80x9cC5+xe2x80x9d) product stream from a given feedstock at a given severity level, or conversely as the temperature required to achieve a given octane number.
2) Selectivity refers to the percentage yield of petrochemical aromatics or C5+ gasoline product from a given feedstock at a particular activity level.
3) Stability refers to the rate of change of activity or selectivity per unit of time or of feedstock processed. Activity stability generally is measured as the rate of change of operating temperature per unit of time or of feedstock to achieve a given C5+ product octane, with a lower rate of temperature change corresponding to better activity stability, since catalytic reforming units typically operate at relatively constant product octane. Selectivity stability is measured as the rate of decrease of C5+ product or aromatics yield per unit of time or of feedstock.
Programs to improve performance of reforming catalysts are being stimulated by the reformulation of gasoline, following upon widespread removal of lead anti-knock additive, in order to reduce harmful vehicle emissions. Gasoline upgrading processes such as catalytic reforming must operate at higher efficiency with greater flexibility in order to meet these changing requirements. Catalyst selectivity is becoming ever more important to tailor gasoline components to these needs while avoiding losses to lower-value products. The major problem facing workers in this area of the art, therefore, is to develop more selective catalysts while maintaining effective catalyst activity and stability.
The art teaches a variety of multimetallic catalysts for the catalytic reforming of naphtha feedstocks. Most of these comprise combinations of platinum-group metals with rhenium and/or Group IVA(IUPAC 14) metals.
U.S. Pat. No. 3,951,868 (Wilhelm) teaches a catalyst comprising platinum, halogen, germanium or tin, and indium, wherein the ratio of indium to platinum-group metal is about 0.1-1:1. U.S. Pat. No. 4,522,935 (Robinson et al.) discloses a catalyst comprising a platinum-group metal, tin, indium, halogen, and a porous support which may comprise alumina. The feature of the catalyst is an atomic ratio of indium to platinum-group metal of more than 1.35, and preferably about 2.55.
U.S. Pat. No. 3,915,845 (Antos) discloses hydrocarbon conversion with a catalyst comprising a platinum-group metal, Group IVA metal, halogen and lanthanide in an atomic ratio to platinum-group metal of 0.1 to 1.25. The preferred lanthanides are lanthanum, cerium, and especially neodymium which was exemplified in Antos. U.S. Pat. No. 4,039,477 (Engelhard et al.) discloses a catalyst for the catalytic hydrotreatment of hydrocarbons comprising a refractory metal oxide, platinum-group metal, tin and at least one metal from yttrium, thorium, uranium, praseodymium, cerium, lanthanum, neodymium, samarium, dysprosium and gadolinium with favorable results being observed at relatively low ratios of the latter metals to platinum.
Another type of multimetallic catalyst has been disclosed as comprising a combination of platinum with rhodium or osmium and a third metal. U.S. Pat. No. 4,401,557 (Juguin et al.) discloses a reforming process using a catalyst comprising a carrier, platinum, a second metal of either rhodium or osmium, and a third metal from the list of chromium, tungsten, molybdenum, manganese, rhenium, gallium, indium, thallium, samarium, zinc, cadmium, titanium, and zirconium. The examples appear to show that the preferred third metals are essentially tungsten, manganese, rhenium, gallium, germanium, tin, thorium, cerium, and samarium.
It is an object of the invention to provide a novel catalyst for improved selectivity in hydrocarbon conversion. A corollary object of the invention is to provide a reforming process having improved selectivity with respect to gasoline or aromatics yields.
The invention originates from the discovery that a catalyst containing platinum, tin, indium and cerium on chlorided alumina shows a favorable ratio of aromatization to cracking in a reforming reaction.
A broad embodiment of the present invention is a catalyst comprising a refractory inorganic oxide, a platinum-group. metal, a Group IVA(IUPAC 14) metal, indium and a lanthanide-series metal. The atomic ratio of the combination of indium and lanthanide metal to platinum-group metal preferably is at least about 1.5, more preferably at least about 2. The catalyst optimally also comprises a halogen, especially chlorine. In preferred embodiments the refractory inorganic oxide is alumina, the platinum-group metal is platinum, the Group IVA(IUPAC 14) metal is tin, and the lanthanide-series metal is cerium. A highly preferred catalyst consists essentially of platinum, tin, indium and cerium on a halogenated alumina support.
In another aspect, the invention is a process for the conversion of a hydrocarbon feedstock utilizing a catalyst comprising a refractory inorganic oxide, a platinum-group metal, a Group IVA(IUPAC 14) metal, indium and a lanthanide-series metal. Preferably the hydrocarbon conversion is catalytic reforming of a naphtha feedstock, utilizing the catalyst of the invention to increase the yield of gasoline and/or aromatics. The conversion optimally comprises dehydrocyclization to increase aromatics yields. In an advantageous embodiment, the naphtha feedstock comprises hydrocarbons in the C6-C8 range which yield one or more of benzene, toluene and xylenes in a catalytic reforming unit.
These as well as other objects and embodiments will become evident from the following more detailed description of the present invention.